1. Field
This disclosure relates generally to pulsed lasers and machining materials using high repetition rate pulsed lasers.
2. Description of the Related Art
Several material processing applications including, for example, thin silicon wafer dicing, printed circuit board (PCB) drilling, solar cell manufacturing, and flat panel display manufacturing, involve similar material processing techniques and problems. Early solutions included mechanical and lithographic processing techniques. However, the reduction in device size, increased device complexity, and the environmental cost of chemical processing transitioned the industry toward laser processing methods. High power diode-pumped solid state lasers having typical wavelengths of 1 μm, or frequency converted versions having green or UV wavelengths, are now utilized. One method utilized in some applications includes progressively cutting through the material with repetitive passes at relatively high scanning speeds. In such applications, there are three main problems: (a) cleaning cutting through the desired material without causing damage to the material (e.g., residual stress, delamination, thermally induced material modification, etc.), (b) achieving a sufficiently high volume material removal rate to be commercially viable, and (c) reduction/elimination of recast material.
Various options have been suggested for efficient and high-quality laser-based machining of materials, including operation at high repetition rates with less debris and melt. However, the problem of limiting accumulation of re-deposited material near a processing site has not been sufficiently addressed, and is generally a difficult problem to overcome. As high material removal rates are required for rapid processing, the relatively large amount of ablated material ejected from a processing site may generally include one or more of liquid melt, relatively large quantities of solid material, and vapor. Fine distributions of particles, down to the nanometer scale (e.g., 10 nm), may also be redeposited.
In various applications, the problem of limiting accumulation has been addressed with process modifications. For example, in some current semiconductor-industry techniques, a substrate may be coated with a sacrificial layer of material that is removed with the redeposited material after laser processing. This process step may be used alone or in combination with post-processing of the substrate with various chemical solvents to remove the recast. However, such techniques reduce throughput and increase costs by adding additional processing steps and additional consumable materials. As such, a preferred solution would eliminate the need for such debris removal.
Process debris may include slag, melted regions, heat-affected zones (HAZ), and so forth. In some cases, the debris cannot be effectively removed using conventional non-chemical cleaning techniques such as, for example, cleaning in an ultrasonic bath.
Moreover, low-k material and composite layers utilized in integrated circuits and semiconductor devices introduce challenges for certain implementations of laser-based material processing. Low-k material can include material that has a dielectric constant that is less than the dielectric constant of silicon dioxide. For example, low-k material can include dielectric materials such as doped silicon dioxide, polymeric dielectrics, etc.